<!DOCTYPE html>
<html lang="zh" dir="ltr" class="client-nojs">
<head>
<title>指针声明</title>
<meta charset="UTF-8">
<meta name="generator" content="MediaWiki 1.21.2">
<link rel="shortcut icon" href="../../../common/favicon.ico">
<link rel="stylesheet" href="../../../common/ext.css">
<meta name="ResourceLoaderDynamicStyles" content="">
<link rel="stylesheet" href="../../../common/site_modules.css">
<style>a:lang(ar),a:lang(ckb),a:lang(fa),a:lang(kk-arab),a:lang(mzn),a:lang(ps),a:lang(ur){text-decoration:none}#toc{display:none}.editsection{display:none}
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-css:7:15cea3ec788a65b5187d4018eed543bf */</style>

<script src="../../../common/startup_scripts.js"></script>
<script>if(window.mw){
mw.config.set({"wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"c/language/pointer","wgTitle":"c/language/pointer","wgCurRevisionId":59523,"wgArticleId":7952,"wgIsArticle":true,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":[],"wgBreakFrames":false,"wgPageContentLanguage":"zh","wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"zh","wgMonthNames":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgMonthNamesShort":["","1月","2月","3月","4月","5月","6月","7月","8月","9月","10月","11月","12月"],"wgRelevantPageName":"c/language/pointer","wgUserVariant":"zh","wgRestrictionEdit":[],"wgRestrictionMove":[]});
}</script><script>if(window.mw){
mw.loader.implement("user.options",function(){mw.user.options.set({"ccmeonemails":0,"cols":80,"date":"default","diffonly":0,"disablemail":0,"disablesuggest":0,"editfont":"default","editondblclick":0,"editsection":0,"editsectiononrightclick":0,"enotifminoredits":0,"enotifrevealaddr":0,"enotifusertalkpages":1,"enotifwatchlistpages":0,"extendwatchlist":0,"externaldiff":0,"externaleditor":0,"fancysig":0,"forceeditsummary":0,"gender":"unknown","hideminor":0,"hidepatrolled":0,"imagesize":2,"justify":0,"math":1,"minordefault":0,"newpageshidepatrolled":0,"nocache":0,"noconvertlink":0,"norollbackdiff":0,"numberheadings":0,"previewonfirst":0,"previewontop":1,"quickbar":5,"rcdays":7,"rclimit":50,"rememberpassword":0,"rows":25,"searchlimit":20,"showhiddencats":0,"showjumplinks":1,"shownumberswatching":1,"showtoc":0,"showtoolbar":1,"skin":"cppreference2","stubthreshold":0,"thumbsize":2,"underline":2,"uselivepreview":0,"usenewrc":0,"watchcreations":0,"watchdefault":0,"watchdeletion":0,
"watchlistdays":3,"watchlisthideanons":0,"watchlisthidebots":0,"watchlisthideliu":0,"watchlisthideminor":0,"watchlisthideown":0,"watchlisthidepatrolled":0,"watchmoves":0,"wllimit":250,"variant":"zh","language":"zh","searchNs0":true,"searchNs1":false,"searchNs2":false,"searchNs3":false,"searchNs4":false,"searchNs5":false,"searchNs6":false,"searchNs7":false,"searchNs8":false,"searchNs9":false,"searchNs10":false,"searchNs11":false,"searchNs12":false,"searchNs13":false,"searchNs14":false,"searchNs15":false,"gadget-MathJax":1,"gadget-ColiruCompiler":1});;},{},{});mw.loader.implement("user.tokens",function(){mw.user.tokens.set({"editToken":"+\\","patrolToken":false,"watchToken":false});;},{},{});
/* cache key: mwiki1-mwiki_zh_:resourceloader:filter:minify-js:7:258d7cd6aa9aa67dee25e01fb6a9e505 */
}</script>
<script>if(window.mw){
mw.loader.load(["mediawiki.page.startup","mediawiki.legacy.wikibits","mediawiki.legacy.ajax"]);
}</script>
<style type="text/css">/*<![CDATA[*/
.source-c {line-height: normal;}
.source-c li, .source-c pre {
	line-height: normal; border: 0px none white;
}
/**
 * GeSHi Dynamically Generated Stylesheet
 * --------------------------------------
 * Dynamically generated stylesheet for c
 * CSS class: source-c, CSS id: 
 * GeSHi (C) 2004 - 2007 Nigel McNie, 2007 - 2008 Benny Baumann
 * (http://qbnz.com/highlighter/ and http://geshi.org/)
 * --------------------------------------
 */
.c.source-c .de1, .c.source-c .de2 {font: normal normal 1em/1.2em monospace; margin:0; padding:0; background:none; vertical-align:top;}
.c.source-c  {font-family:monospace;}
.c.source-c .imp {font-weight: bold; color: red;}
.c.source-c li, .c.source-c .li1 {font-weight: normal; vertical-align:top;}
.c.source-c .ln {width:1px;text-align:right;margin:0;padding:0 2px;vertical-align:top;}
.c.source-c .li2 {font-weight: bold; vertical-align:top;}
.c.source-c .kw1 {color: #0000dd;}
.c.source-c .kw2 {color: #0000ff;}
.c.source-c .kw3 {color: #0000dd;}
.c.source-c .kw4 {color: #0000ff;}
.c.source-c .co1 {color: #909090;}
.c.source-c .co2 {color: #339900;}
.c.source-c .coMULTI {color: #ff0000; font-style: italic;}
.c.source-c .es0 {color: #008000; font-weight: bold;}
.c.source-c .es1 {color: #008000; font-weight: bold;}
.c.source-c .es2 {color: #008000; font-weight: bold;}
.c.source-c .es3 {color: #008000; font-weight: bold;}
.c.source-c .es4 {color: #008000; font-weight: bold;}
.c.source-c .es5 {color: #008000; font-weight: bold;}
.c.source-c .br0 {color: #008000;}
.c.source-c .sy0 {color: #008000;}
.c.source-c .sy1 {color: #000080;}
.c.source-c .sy2 {color: #000040;}
.c.source-c .sy3 {color: #000040;}
.c.source-c .sy4 {color: #008080;}
.c.source-c .st0 {color: #008000;}
.c.source-c .nu0 {color: #000080;}
.c.source-c .nu6 {color:#000080;}
.c.source-c .nu8 {color:#000080;}
.c.source-c .nu12 {color:#000080;}
.c.source-c .nu16 {color:#000080;}
.c.source-c .nu17 {color:#000080;}
.c.source-c .nu18 {color:#000080;}
.c.source-c .nu19 {color:#000080;}
.c.source-c .ln-xtra, .c.source-c li.ln-xtra, .c.source-c div.ln-xtra {background-color: #ffc;}
.c.source-c span.xtra { display:block; }

/*]]>*/
</style><!--[if lt IE 7]><style type="text/css">body{behavior:url("/mwiki/skins/cppreference2/csshover.min.htc")}</style><![endif]--></head>
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_language_pointer skin-cppreference2 action-view cpp-navbar">
        <!-- header -->
        <!-- /header -->
        <!-- content -->
<div id="cpp-content-base">
            <div id="content">
                <a id="top"></a>
                <div id="mw-js-message" style="display:none;"></div>
                                <!-- firstHeading -->
<h1 id="firstHeading" class="firstHeading">指针声明</h1>
                <!-- /firstHeading -->
                <!-- bodyContent -->
                <div id="bodyContent">
                                        <!-- tagline -->
                    <div id="siteSub">来自cppreference.com</div>
                    <!-- /tagline -->
                                        <!-- subtitle -->
                    <div id="contentSub"><span class="subpages">&lt; <a href="../../c.html" title="c">c</a>‎ | <a href="../language.html" title="c/language">language</a></span></div>
                    <!-- /subtitle -->
                                                            <!-- bodycontent -->
                    <div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../../c.html" title="c"> C</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
<tr class="t-nv"><td colspan="5"> <a href="../language.html" title="c/language">语言</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../header.html" title="c/header">头文件</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../types.html" title="c/types">类型支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../program.html" title="c/program">程序工具</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../variadic.html" title="c/variadic">变参数函数支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../memory.html" title="c/memory">动态内存管理</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../error.html" title="c/error">错误处理</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../chrono.html" title="c/chrono">日期和时间工具</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../string.html" title="c/string">字符串库</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../algorithm.html" title="c/algorithm">算法</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../numeric.html" title="c/numeric">数值</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../io.html" title="c/io">输入/输出支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../locale.html" title="c/locale">本地化支持</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../thread.html" title="c/thread">线程支持</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../atomic.html" title="c/atomic">原子操作</a> <span class="t-mark-rev t-since-c11">(C11)</span> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="../experimental.html" title="c/experimental">技术规范</a> </td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../language.html" title="c/language">C 语言</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-h2"><td colspan="5"> <a href="basic_concepts.html" title="c/language/basic concepts">基本概念</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../keyword.html" title="c/keyword">关键词</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../preprocessor.html" title="c/preprocessor">预处理器</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="statements.html" title="c/language/statements">语句</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="expressions.html" title="c/language/expressions">表达式</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="initialization.html" title="c/language/initialization">初始化</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="declarations.html" title="c/language/declarations">声明</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="functions.html" title="c/language/functions">函数</a></td></tr>
<tr class="t-nv"><td colspan="5"> 杂项</td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="history.html" title="c/language/history">C 的历史</a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> <a href="../experimental.html" title="c/experimental">技术规范</a> </td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="declarations.html" title="c/language/declarations">声明</a><div class="t-navbar-menu"><div><div style="display:inline-block">
<div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <strong class="selflink">指针</strong> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="array.html" title="c/language/array">数组</a> </td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="enum.html" title="c/language/enum"><span class="t-lines"><span>enum</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="struct.html" title="c/language/struct"><span class="t-lines"><span>struct</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="union.html" title="c/language/union"><span class="t-lines"><span>union</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="bit_field.html" title="c/language/bit field">位域</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="atomic.html" title="c/language/atomic">原子类型</a> <span class="t-mark-rev t-since-c11">(C11)</span></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="const.html" title="c/language/const"><span class="t-lines"><span>const</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="volatile.html" title="c/language/volatile"><span class="t-lines"><span>volatile</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="restrict.html" title="c/language/restrict"><span class="t-lines"><span>restrict</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="_Alignas.html" title="c/language/ Alignas"><span class="t-lines"><span>_Alignas</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="storage_duration.html" title="c/language/storage duration">存储期与链接</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="extern.html" title="c/language/extern">外部及试探性定义</a> </td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="typedef.html" title="c/language/typedef"><span class="t-lines"><span>typedef</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="_Static_assert.html" title="c/language/ Static assert"><span class="t-lines"><span>_Static_assert</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div></div></td></tr>
</table></div>
</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>指针是一种对象类型，它引用函数或另一种类型的对象，可以添加限定符。指针亦可以不引用任何内容，这通过一个特定的空指针值指示。
</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
<p>在指针声明的<a href="declarations.html" title="c/language/declarations">声明文法</a>中，<i>类型指定符</i>序列指代所指向的类型（可以是函数或对象，可以是不完整类型），而<i>声明器</i>拥有形式：
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>*</b></code> <span class="t-spar">qualifiers</span><span class="t-mark">(可选)</span> <span class="t-spar">declarator</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中 <span class="t-spar">declarator</span> 可以是命名所声明指针的标识符，包括另一个指针声明器（这指示一个指向指针的指针）：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">float</span> <span class="sy2">*</span>p, <span class="sy2">**</span>pp<span class="sy4">;</span> <span class="co1">// p 是指向 float 的指针</span>
                <span class="co1">// pp 是指向指向 float 指针的指针</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>fp<span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// fp 是指向类型 int(int) 为函数的指针</span></pre></div></div>
<p>出现在 <code><b>*</b></code> 与标识符（或另一个嵌套声明器）间的 <span class="t-spar">qualifiers</span> 将被声明的限定赋予指针类型：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n<span class="sy4">;</span>
<span class="kw4">const</span> <span class="kw4">int</span> <span class="sy2">*</span> pc <span class="sy1">=</span> <span class="sy3">&amp;</span>n<span class="sy4">;</span> <span class="co1">// pc 是指向 const int 的非 const 指针</span>
<span class="co1">// *pc = 2; // 错误：不能通过不带转型的 p 修改 n</span>
pc <span class="sy1">=</span> <a href="../types/NULL.html"><span class="kw103">NULL</span></a><span class="sy4">;</span> <span class="co1">// OK ： pc 自身可修改</span>
 
<span class="kw4">int</span> <span class="sy2">*</span> <span class="kw4">const</span> cp <span class="sy1">=</span> <span class="sy3">&amp;</span>n<span class="sy4">;</span> <span class="co1">// cp 是一个指向非 const 的 int 的 const 指针</span>
<span class="sy2">*</span>cp <span class="sy1">=</span> <span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// OK ：通过 cp 修改 n</span>
<span class="co1">// cp = NULL; // 错误： cp 自身不能修改</span>
 
<span class="kw4">int</span> <span class="sy2">*</span> <span class="kw4">const</span> <span class="sy2">*</span> pcp <span class="sy1">=</span> <span class="sy3">&amp;</span>cp<span class="sy4">;</span> <span class="co1">// 指向指向非 const 的 int 的 const 指针的非 const 指针</span></pre></div></div>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<p>指针用于间接使用，这是种普遍存在的编程技巧；它们可以用于实现按引用传递语义、访问有动态<a href="storage_duration.html" title="c/language/storage duration">存储期</a>的对象、实现“可选”类型（使用空指针值）、结构体间的聚合关系、回调（使用指向函数指针）、泛型接口（使用指向 void 的指针）以及其他更多。
</p>
<h4><span class="mw-headline" id=".E6.8C.87.E5.90.91.E5.AF.B9.E8.B1.A1.E7.9A.84.E6.8C.87.E9.92.88">指向对象的指针</span></h4>
<p>指向对象的指针可以通过应用于对象类型（可以不完整）表达式的<a href="operator_member_access.html" title="c/language/operator member access">取值运算符</a>初始化：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n<span class="sy4">;</span>
<span class="kw4">int</span> <span class="sy2">*</span>np <span class="sy1">=</span> <span class="sy3">&amp;</span>n<span class="sy4">;</span> <span class="co1">// 指向 int 的指针</span>
<span class="kw4">int</span> <span class="sy2">*</span><span class="kw4">const</span> <span class="sy2">*</span>npp <span class="sy1">=</span> <span class="sy3">&amp;</span>np<span class="sy4">;</span> <span class="co1">// 指向指向非 const 的 int 的 const 指针的非 const 指针</span>
 
<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>ap<span class="br0">)</span><span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span> <span class="sy1">=</span> <span class="sy3">&amp;</span>a<span class="sy4">;</span> <span class="co1">// 指向 int 数组的指针</span>
 
<span class="kw1">struct</span> S <span class="br0">{</span> <span class="kw4">int</span> n<span class="sy4">;</span> <span class="br0">}</span> s <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span>
<span class="kw4">int</span><span class="sy2">*</span> sp <span class="sy1">=</span> <span class="sy3">&amp;</span>s.<span class="me1">n</span><span class="sy4">;</span> <span class="co1">// 指向作为 s 成员的 int 的指针</span></pre></div></div>
<p>指针可以出现作<a href="operator_member_access.html#.E8.A7.A3.E5.BC.95.E7.94.A8" title="c/language/operator member access">间接运算符</a> （一元 <code><b>*</b></code> ）的运算数，它返回标识所指向对象的<a href="value_category.html" title="c/language/value category">左值</a>：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n<span class="sy4">;</span>
<span class="kw4">int</span><span class="sy2">*</span> p <span class="sy1">=</span> <span class="sy3">&amp;</span>n<span class="sy4">;</span>     <span class="co1">// 指针 p 指向 n</span>
<span class="sy2">*</span>p <span class="sy1">=</span> <span class="nu0">7</span><span class="sy4">;</span>         <span class="co1">// 存储 7 于 n</span>
<a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%d<span class="es1">\n</span>"</span>, <span class="sy2">*</span>p<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 左值到右值转换从 n 读取值</span></pre></div></div>
<p>指向 <a href="struct.html" title="c/language/struct">struct</a> 和 <a href="union.html" title="c/language/union">union</a> 类型对象的指针亦可作为<a href="operator_member_access.html" title="c/language/operator member access">经由指针成员访问</a>运算符 <code><b>-&gt;</b></code> 的左运算数出现。
</p><p>因为<a href="array.html#.E6.95.B0.E7.BB.84.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2" title="c/language/array">数组到指针</a>隐式转换，指向数组首元素的指针可通过数组类型表达式初始化：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span>
<span class="kw4">int</span> <span class="sy2">*</span>p <span class="sy1">=</span> a<span class="sy4">;</span> <span class="co1">// 指向a[0]</span>
 
<span class="kw4">int</span> b<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span><span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span><span class="sy4">;</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>row<span class="br0">)</span><span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span> <span class="sy1">=</span> b<span class="sy4">;</span> <span class="co1">// 指向b[0]</span></pre></div></div>
<p>确定的<a href="operator_arithmetic.html" title="c/language/operator arithmetic">加减</a>、<a href="operator_assignment.html" title="c/language/operator assignment">复合赋值</a>、<a href="operator_incdec.html" title="c/language/operator incdec">自增减</a>运算符定义于指向数组元素的指针。
</p><p><a href="operator_comparison.html" title="c/language/operator comparison">比较运算符</a>在一些情况下定义于指向对象的指针：二个表示相同地址的指针比较相等，二个空指针值比较相等，比较指向同一数组的元素的指针以二个元素的数组下标比较，及指向结构体成员的指针以这些成员声明顺序比较。
</p><p>许多实现亦提供随意来源指针的<a href="https://en.wikipedia.org/wiki/Total_order#Strict_total_order" class="extiw" title="enwiki:Total order">严格全序</a>，例如若它们实现在连续（“平直”）的虚拟地址空间上。
</p>
<h4><span class="mw-headline" id=".E6.8C.87.E5.90.91.E5.87.BD.E6.95.B0.E7.9A.84.E6.8C.87.E9.92.88">指向函数的指针</span></h4>
<p>指向函数的指针可由函数地址初始化。因为<a href="conversion.html#.E5.87.BD.E6.95.B0.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2" title="c/language/conversion">函数到指针</a>转换，取址运算符是可选的：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">void</span> <span class="br0">(</span><span class="sy2">*</span>pf1<span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> <span class="sy3">&amp;</span>f<span class="sy4">;</span>
<span class="kw4">void</span> <span class="br0">(</span><span class="sy2">*</span>pf2<span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> f<span class="sy4">;</span> <span class="co1">// 等于&amp;f</span></pre></div></div>
<p>不同于函数，指向函数的指针是对象，从而能存储在数组中、复制、赋值、作为参数传递给其他函数等等。
</p><p>指向函数的指针可以用作<a href="operator_other.html#.E5.87.BD.E6.95.B0.E8.B0.83.E7.94.A8" title="c/language/operator other">函数调用运算符</a>的左运算数；这会调用所指向的函数：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="kw4">int</span> f<span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%d<span class="es1">\n</span>"</span>, n<span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">return</span> n<span class="sy2">*</span>n<span class="sy4">;</span>
<span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>p<span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> f<span class="sy4">;</span>
    <span class="kw4">int</span> x <span class="sy1">=</span> p<span class="br0">(</span><span class="nu0">7</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>解引用函数指针产生所指向函数的函数指代器：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> f<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>p<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">=</span> f<span class="sy4">;</span>    <span class="co1">// 指针 p 指向 f</span>
<span class="br0">(</span><span class="sy2">*</span>p<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 通过函数指代器调用函数 f</span>
p<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>    <span class="co1">// 直接通过指针调用 f</span></pre></div></div>
<p><a href="operator_comparison.html" title="c/language/operator comparison">等于比较运算符</a>定义于指向函数的指针（若指向相同函数则它们比较相等）。
</p><p>因为<a href="type.html#.E5.85.BC.E5.AE.B9.E7.B1.BB.E5.9E.8B" title="c/language/type" class="mw-redirect">函数类型的兼容性</a>忽略函数参数的顶层限定符，指向仅在参数的顶层限定符有区别的函数指针是可互换的：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> f<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span>, fc<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>pc<span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> f<span class="sy4">;</span> <span class="co1">// OK</span>
<span class="kw4">int</span> <span class="br0">(</span><span class="sy2">*</span>p<span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy1">=</span> fc<span class="sy4">;</span>       <span class="co1">// OK</span>
pc <span class="sy1">=</span> p<span class="sy4">;</span>                   <span class="co1">// OK</span></pre></div></div>
<h4><span class="mw-headline" id=".E6.8C.87.E5.90.91_void_.E6.8C.87.E9.92.88">指向 void 指针</span></h4>
<p>指向任意类型对象的指针能<a href="conversion.html" title="c/language/conversion">隐式转换</a>成指向 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span></span></span> 的指针（可选地有 <a href="const.html" title="c/language/const">const</a> 或 <a href="volatile.html" title="c/language/volatile">volatile</a> 限定），反之亦然：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> n<span class="sy1">=</span><span class="nu0">1</span>, <span class="sy2">*</span>p<span class="sy1">=</span><span class="sy3">&amp;</span>n<span class="sy4">;</span>
<span class="kw4">void</span><span class="sy2">*</span> pv <span class="sy1">=</span> p<span class="sy4">;</span> <span class="co1">// int* 到 void*</span>
<span class="kw4">int</span><span class="sy2">*</span> p2 <span class="sy1">=</span> pv<span class="sy4">;</span> <span class="co1">// void* 到 int*</span>
<a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%d<span class="es1">\n</span>"</span>, <span class="sy2">*</span>p2<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印 1</span></pre></div></div>
<p>指向 void 的指针用于传递未知类型的对象，这在泛型接口中常用： <span class="t-lc"><a href="../memory/malloc.html" title="c/memory/malloc">malloc</a></span> 返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span><span class="sy2">*</span></span></span> ，<span class="t-lc"><a href="../algorithm/qsort.html" title="c/algorithm/qsort">qsort</a></span> 期待用户提供接受二个 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span></span></span> 参数的回调。 <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_create.html">pthread_create</a> 期待用户提供接受并返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">void</span><span class="sy2">*</span></span></span> 的回调。所有情况下，调用方负责在使用前将指针转换到正确的类型。
</p>
<h3><span class="mw-headline" id=".E7.A9.BA.E6.8C.87.E9.92.88">空指针</span></h3>
<p>每种类型的指针都有含有一个该类型的特殊的值，称为<i>空指针值</i>。值为空的指针不指向对象或函数（解引用空指针是未定义行为），而且与所有相同类型的且值以为<i>空</i>的指针比较相等。
</p><p>为初始化指针为空，或将空值赋给已存在的指针，可以使用空指针常量（ <span class="t-lc"><a href="../types/NULL.html" title="c/types/NULL">NULL</a></span> ，或其他任何拥有值零的整数常量）。<a href="initialization.html" title="c/language/initialization">静态初始化</a>亦将指针初始化到它们的空值。
</p><p>空指针可以指示对象不存在，或可用于指示错误条件的其他对象。通常，接收指针参数的函数几乎总是需要检查该值是否为空，并对该情况特殊处理（例如， <span class="t-lc"><a href="../memory/free.html" title="c/memory/free">free</a></span> 在传递空指针时不做任何事）。
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
<p>尽管任何指向对象的指针<a href="cast.html" title="c/language/cast">能被转型</a>成指向其他类型对象的指针，解引用指向类型异于对象声明类型的指针几乎总是未定义行为。细节见<a href="object.html#.E4.B8.A5.E6.A0.BC.E5.88.AB.E5.90.8D.E4.BD.BF.E7.94.A8" title="c/language/object">严格别名使用</a>。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>可以指示函数，通过不会有别名使用的指针访问对象。细节见 <a href="restrict.html" title="c/language/restrict"><code>restrict</code></a> 。
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td></tr>
</table>
<p>数组类型的左值表达式，在大多数语境中使用时，会经历<a href="conversion.html" title="c/language/conversion">隐式转换</a>到指向数组首元素的指针。细节见<a href="array.html#.E6.95.B0.E7.BB.84.E5.88.B0.E6.8C.87.E9.92.88.E8.BD.AC.E6.8D.A2" title="c/language/array">数组到指针转换</a>。
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">char</span> <span class="sy2">*</span>str <span class="sy1">=</span> <span class="st0">"abc"</span><span class="sy4">;</span> <span class="co1">// "abc" 是 char[4] 类型的数组， str 是指向 'a' 的指针</span></pre></div></div>
<p>指向 char 的指针通常<a href="../string/byte.html" title="c/string/byte">用于表示字符串</a>。为表示合法的字节字符串，指针必须指向作为 char 数组元素的 char ，而且在大于或等于指针所引用元素的下标的某个下标处，必须有零值的 char 。
</p>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.7.6.1 Pointer declarators (p: 130)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.7.5.1 Pointer declarators (p: 115-116)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 3.5.4.1 Pointer declarators 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table></div>
</div>

<!-- 
NewPP limit report
Preprocessor visited node count: 2203/1000000
Preprocessor generated node count: 5970/1000000
Post‐expand include size: 46016/2097152 bytes
Template argument size: 8724/2097152 bytes
Highest expansion depth: 16/40
Expensive parser function count: 0/100
-->

<!-- Saved in parser cache with key mwiki1-mwiki_zh_:pcache:idhash:7952-0!*!0!!zh!*!zh!* and timestamp 20200216161915 -->
</div>                    <!-- /bodycontent -->
                                        <!-- printfooter -->
                    <div class="printfooter">
                    来自“<a href="https://zh.cppreference.com/mwiki/index.php?title=c/language/pointer&amp;oldid=59523">https://zh.cppreference.com/mwiki/index.php?title=c/language/pointer&amp;oldid=59523</a>”                    </div>
                    <!-- /printfooter -->
                                                            <!-- catlinks -->
                    <!-- /catlinks -->
                                                            <div class="visualClear"></div>
                    <!-- debughtml -->
                                        <!-- /debughtml -->
                </div>
                <!-- /bodyContent -->
            </div>
        </div>
        <!-- /content -->
        <!-- footer -->
        <div id="cpp-footer-base" class="noprint">
            <div id="footer">
                        <div id="cpp-navigation">
            <h5>导航</h5>
            <ul><li><a href="https://zh.cppreference.com/w/c/language/pointer">Online version</a></li><li>Offline version retrieved 2020-03-14 18:00.</li></ul></div>
                        <ul id="footer-info">
                                    <li id="footer-info-lastmod"> 本页面最后修改于2019年3月4日 (星期一) 01:00。</li>
                                    <li id="footer-info-viewcount">此页面已被浏览过3,401次。</li>
                            </ul>
                    </div>
        </div>
        <!-- /footer -->
        <script>if(window.mw){
mw.loader.state({"site":"loading","user":"missing","user.groups":"ready"});
}</script>
<script src="../../../common/skin_scripts.js"></script>
<script>if(window.mw){
mw.loader.load(["mediawiki.action.view.postEdit","mediawiki.user","mediawiki.page.ready","mediawiki.searchSuggest","mediawiki.hidpi","ext.gadget.MathJax","ext.gadget.ColiruCompiler"], null, true);
}</script>
<script src="../../../common/site_scripts.js"></script>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-2828341-1']);
_gaq.push(['_setDomainName', 'cppreference.com']);
_gaq.push(['_trackPageview']);
</script><!-- Served in 0.687 secs. -->
	</body>
<!-- Cached 20200216161915 -->
</html>